1. Technical Field
The present development relates to controlling inlet temperature of gases supplied to an exhaust turbine such that the inlet temperature is below a temperature at which the turbine is damaged.
2. Background Art
The exhaust from a turbocharged engine is supplied to the turbine portion of the turbocharger. When the temperature of the exhaust gases at the turbine inlet exceeds a hardware limit temperature of the turbine, measures are taken to reduce turbine inlet temperature. It is known in the prior art to reduce the amount of torque produced by the engine by a predetermined amount from the operator demanded torque so that the exhaust temperature drops below the hardware limit temperature. However, the problems with this approach include: dropping torque in a stepwise manner is noticeable and disconcerting to the vehicle operator; and reducing torque in an open-loop manner leads to overcompensation (too much torque drop) at some operation conditions and undercompensation (failing to protect turbine) at other operating conditions. To avoid undercompensation, the amount of torque reduction is selected to provide an adequate safety factor for the most demanding condition, which is excessive for most operating conditions.
In other strategies, the engine is controlled closed-loop based on an error between a control temperature and the turbine inlet temperature. However, because of thermal inertia in the system, turbine inlet temperature overshoots the control temperature markedly even when a mitigating measure is initiated. If the control temperature is set equal to the maximum hardware temperature, a significant risk of damage to the turbine is incurred during the period of overshoot. If, alternatively, the control temperature is a temperature below the maximum hardware temperature to provide a margin of safety for the turbine, then the steady state temperature achieved is lower than need be and thus, the amount of mitigation (torque reduction or adjustment of another engine parameter) is greater than necessary.